WASHINGTON, July 20 (Reuters) - U.S. President Barack Obama told Israeli Prime Minister Benjamin Netanyahu on Sunday that he has serious concerns about the rising number of casualties from clashes between Israel and the Palestinians.

Obama spoke by telephone to Netanyahu for the second time in three days. He told him Israel has the right to defend itself and he reiterated U.S. condemnation of attacks by Hamas against Israel.

"The president also raised serious concern about the growing number of casualties, including increasing Palestinian civilian deaths in Gaza and the loss of Israeli soldiers," the White House said in a statement describing the conversation.

More than 60 Palestinians and 13 Israeli soldiers were killed as Israel shelled a Gaza neighborhood and battled militants on Sunday in the bloodiest fighting in a nearly 2-week-old offensive.

Obama told Netanyahu that U.S. Secretary of State John Kerry will travel to Cairo soon to seek an immediate cessation of hostilities based on a return to a November 2012 ceasefire agreement.

"The president underscored that the United States will work closely with Israel and regional partners on implementing an immediate ceasefire, and stressed the need to protect civilians - in Gaza and in Israel," the statement said. (Reporting by Steve Holland; Editing by Doina Chiacu)